Production of ferrous sulphate monohydrate



Feb. 26, 1946. D. EDGE PRODUCTION OF'FERROUS SULPHATE MONOHYDRATE vFiled Feb. 5, 1944 INVENTOR; 05 72? [065, BY 5 I ORNEY end to form F8804crystals, but

Patented Feb. 26, 1946 PRODUCTION OF FERROUS SULPHATE MON OHYDRATEDexter Edge, Gary, Ind.

Application February 5, 1944, Serial No. 521,253 (Cl. 23-126) 4 Claims.

This invention relates to the production of ferrous sulphatemonohydrate, and more particularly to the recovery thereof from wastepickle liquor and i a continuation-in-part of my patent ap- 1 plicationNo. 422,304, filed December 9, 1941.

In the cleaning of various metallic articles, there is used a picklingsolution comprised of sulphuric acid, From this pickling solution thereresults a product known as pickle liquor which includes in solution ironand acid.

Fora number of years the disposition of pickle liquor has been an acuteproblem. One method of disposal i to treat it in such manner as toproduce ferrous sulphate monohydrate. For the most part, theseoperations have been on a laboratory scale, but they have successfullydemonstrated that the monohydrate can be produced.

The disposal of pickle liquor is more involved than merely removing theferrous sulphate monohydrate; for example, copper-bearing steels arefrequently pickled, and in such case it is necessary to remove theresultant copper sulphate from the pickle liquor;

It is known that the solubility of copper sulphate increases with thetemperature, and this characteristic indicates that around 290 F. to 350F. the ferrous sulphate monohydrate will settle out and leave the coppersulphate in solution.

One method which may be employed for the commercial production offerrous sulphate monohydrate relies upon the principle of sedimentation,but so far as I am aware it has been confined to treatment in batches.It is apparent that such a method of manufacture is limited in outputdue to the time required to bring each batch to reaction temperature,settling, removing emptying, and replacing the receptacles. In addition, unusual precautions must be taken to provide equipment which canbe safely handled to prevent serious burning of the operators by hotliquid at high pressures, such as a temperature of around 350 F. andpressure in the nature of 120-140 pounds per square inch.

At the cooling end, ferrous sulphate exists as 7(H2O)FeSO4; at the peaksolubility as 4(H2O) F6804, and at the high temperature end as1(H2O)FBSO4, the monohydrate being completely insoluble at 290 F.

It has previously been proposed, in the treatment of waste pickleliquor, to use the cooling if the cooling plan i used the coppersulphate and iron sulphate will both settle out as crystals, which willbe contaminated. The cooling method also requires ice machinery. Inaddition, the combined heat and cooling cycle results in excessive heatloss.

It is among the objects of the present invention to produce ferroussulphate monohydrate from waste pickle liquor by adopting thehigh-temperature crystallization of the monohydrate whereby there ispermitted, if desired, electrolytic copper refining to remove any coppersulphate from the returning pickle liquor which has been freed offerrous sulphate.

Another object is to provide a method of the foregoing type which iswell adapted to an eflective heat cycle such as will allow heatexchanges to maintain temperature levels at each point at the minimumheat required.

Another object is to provide a continuous system of production whichwill permit the uninterrupted return of the pickle liquor after theferrous sulphate has been removed.

The invention, then, comprises the features hereinafter fully describedand as particularly pointed out in the claims, the following descriptionand the annexed drawing setting forth in detail a certain illustrativeembodiment of th invention, this being indicative done of the number ofways in which the principles of the invention may be employed.

In said drawing, the single figure is a diagrammatic view of theapparatus of the present invention, illustrating the sedimentation tankand its heating instrumentalities in section.

Referring more particularly to the drawing, wherein there is illustratedapparatus which may be employed in the practice of the presentinvention, the numeral 2 designates a pickling tank through which theworkpiece, such as strip metal X, is adapted to be passed and pickled inaccord ance with well-known practice. This pickling tank 2 is suppliedwith make-up pickling acid through a, pipe 3. Communicating with thebottom of the pickling tank 2 is an outlet pipe l which passes through aheat exchanger 5 and connect with a waste pickle liquor manifold 6.-Through a pipe J, the waste pickle liquor manifold 6 is connected to awaste pickle liquor storage vat 8.

A pump I0 is connected to the waste pickle liquor storage vat 8, andserves to boost the waste pickle liquor to a pressure of about poundsper square inch and force it through a. pipe i8 which passes through aheat exchanger i4, steam heater l5, and enters the top of asedimentation tank l6. p

Within the sedimentation tank l6 and adjacent the top thereof is adischarge nozzle l'|- lower portion of the bailie I8 is provided with aflared skirt l9 which extends into close proximity to the walls of thesedimentation tank, and whose sloping outer surface forms one side of apassageway 20 located between the skirt and wall of the tank |6.

The lower ortion 2| of the sedimentation tank I6 is of inverted coneshape, and terminates in a discharge opening 22. Mounted in thisdischarge opening 22 is a float controlled valve 23 which is disposedover the opening or expanding nozzle 25 of a collecting chamber 26. Thenozzle 25 is so shaped as to permit rapid separation or escape of steamfrom the discharged crystals. Associated with this collecting chamber 26is 'a briquetting machine 21 wherein the ferrous sulphate monohydrate isformed into cakes for ease of handling, etc.

Disposed on the exterior of the sedimentation tank l6 and adjacent thebottom of the flared skirt I9 of the large conical baflle I8 is a hotwater jacket 30. Another hot water jacket 3| is disposed peripherally ofthe sedimentationtank H5 at a point adjacent the discharge opening 22 inthe bottom thereof. A third but water jacket 32 is disposed between theopening 25 of the collecting chamber 26 and the float controlled'valve23 in the discharge opening 22. jackets 30-3|-32 are connectedsuccessively by a line 34 which passes through a temperature controlledvalve 35. the heat exchangers I4 and 5, and connects with the picklingtank 2, whereby it may be used for hot make-up water. Steam is suppliedto the heat exchanger l4 and steam heater l5 by a steam line 36 whichpasses through a temperature controlled valve 31; and steam is suppliedto the hot water jacket 30, and accordingly the hot water jackets 3| and32, from the steam heater l5 by a pipe 38. The valve 35 controls thetemperature within the tank It by regulating the discharge of the returnpipe'34,

All of the exposed heating surfaces of the sedimentation tank I6 arecovered with a suitable heat insulating medium (not shown) in order toreduce heat loss to a minimum.

The operation of the device is as follows:

From continued use, the acid in tank 2 becomes ineifective and isdrained off through pipe 4 to the settling tank 8 where foreignsubstances in the form of sludge settle out and accumulate in the bottomof the tank. During passage through the heat exchanger 5, thetemperature of the acid is lowered; this hastening the settlingoperation, The clear solution is withdrawn from the tank 8 by the pump land passes through the.

pipe l3, the heat exchanger l4 and the heater l5. During its passagethrough the heat exchanger l4 and heater IS the temperature of the wastepickle liquor is raised to at least 290 F. and is discharged into thepressure vessel I6 at this temperature and at a pressure of preferably160 pounds, and at any rateat a minimum of 120 to 140 pounds per squareinch to prevent boiling of the liquor. As the liquor passes through theheater I and is raised to a temperature of 290 F. there is an initialtendency for the crystals to form. but this tendency is discouraged bythe velocity of the liquor within the pipe l3. The heated liquor entersthe top of, the cone la in the form of horizontal jets 4| which radiatefrom These hot water the pipe I3 and is deflected downwardly toward 4the skirt |9 when it strikes the side of the cone I8. As the liquor isdischarged into the space 50 its velocity is decreased and the smallcrystals drop downwardly out or the path of the movin liquor. Asexplained above, the skirt has formed in conjunction with the body ofthe vessel IS a passage 20 in which an upward flow of liquor toward thereturn pipe 40 is created by the internal pressure of the vessel. Uponreaching the end of the skirt, the descending liquor executes a reversalof flow of 180 because of the current existing in the upwardly movingliquor in the passage 20. At the time of reversal of flow the crystalsformed by chemical reaction become detached from the liquor stream andsettle toward the bottom of the vessel in funnel 2| where they form intoa mound-shaped mass 43. The height of thismound is maintained at apredetermined level by the float 45, which is heavier than the solutionand rests on the mound 43. As the height of the mound varies, the floatmoves the electrical contact 46 to vary the control 41 for the valveoperating motor 49 which controls the movement of the valve 23 toregulate the discharge of the formed crystals, Regulation of the heightof the mound maintains the required space 50 between the mound and theskirt for the formation of crystals. As mentioned above,

the initial tendency for crystal formation is imparted to the liquor inheater I5 andthis tendency is increased within the inverted cone i8 to adegree where the crystals actually form and start settling out. Duringpassage of the crystals through the liquor while settling out (which isa form of migration) crystal growth is accelerated by close associationof the formative ingredients present and the resultantly formed crystalsare deposited on the mound 43. As the mound increases in height, theweight of the crystals compresses the lower portion of the mass to suchan extent that a large portion of the liquid remaining in the crystalsis expelledrand flows upwardly along the-sides of the vessel tointermingle with the returning liquor in the passage 28.

The relatively dry crystals in the bottom of the funnel 2| and exitpassage 22 are maintained at 290 F. by the manifold 3| of the heatingsystem as is also the expanding nozzle 25 in the crystal box 26 by themanifold 32.

The free sulphuric acid remaining after the crystals separate bysedimentation returns through the pipe 40 and the heat exchangers l4 and5 to the picklin tank 2. A regulator 5| is included in the line 40 sothat the pressure in the vessel 5 is maintained at 160 pounds which issufficient to prevent boiling of the liquor. It will be understood thatthe temperature in the vessel |6 is constantly maintained at a minimumof 290 F. by means of the heating manifolds 30 and 3| and that boilingof the contents is prevented by the internal pressure which ismaintained at I pounds by means of the pump l0 and pressure Theefliciency of the systemis increased by using the exhaust steam from theheating system of the pressure vessel IS in the heat exchangers l4 and 5and then discharging the steam in the form of hot condensate to thepickling tank 2. The returning liquor in the pipe 40 is heated in theheat exchangers and 5.

From the foregoing, it will be perceived that the system is continuousand allows an uninterrupted return of pickle liquor freed of the ferroussulphate monohydrate but containing free acid to the pickling tank 2;and there is permitted the maintenance of the pickle Baumat the pointmost effective for the fastest and best pickling. If desired, coppersulphate may be removed from the pickle liquor returning through thepipe 40, for example, by electrolytic copper refining, but as such thisforms no part oi the present invention and is neither shown nordescribed.

While I have 'shown and described a specific embodiment of the presentinvention.- it will be seen that I do not wish to be limited exactlythereto, since various modifications may be made without departing fromthe scope of the invention as defined in the appended claims.

I claim:

1. The continuous method of producing ferrous sulphate monohydrat frompickle liquor containing acid, which includes heating the pickle liquorto above approximately 290 F., while maintaining the liquor at apressure sufficient to prevent formation of steam, directing flow of theheated pickle liquor into an enlarged pressure vessel so as to reducethe velocity oi the pickle liquor and reversing the flow in saidpressure vessel so as to cause the crystals formed at said temperatureto separate by sedimentation, separating out the ferrous sulphatemonohydrate thus formed while maintaining the liquor at the abovetemperature and pressure, and withdrawing residual liquor and free acidfrom the pressure vessel.

2. The continuous method of producing ferrous sulphate monohydrate frompickle liquor containingacid, which includes heating the pickleliquor-to above approximately 290 F. while maintaining the liquor at apressure sumcient to prevent formation of steam, directing flow of theheated pickle liquor into an enlarged pressure vessel so as to reducethe velocity of the pickle liquor and reversing the flow in saidpressure vessel so as to cause the crystals formed at said temperatureto separate by sedimentation, separating out the ferrous sulphatemonohydrate thus formed while maintaining the liquor at the abovetemperature and pressure, withdrawing the ferrous sulphate monohydratefrom the bottom of the pressure vessel, and withdrawing residual liquorand free acid from the pressure vessel.

3. The continuous method of producing ferrous sulphate proximately 290F. while maintainingtheliquor at a pressure sufficient to preventformation of steam, directing flow of the heated pickle liquor into anenlarged pressure vessel so as to reduce the velocity of the pickleliquor and reversing the flow in said pressure vessel so as to cause thecrystals formed at s'aidtemperature to separate by sedimentation,separating out the ferrous sulphate monohydrate thus formed whilemaintaining the liquor at the above temperature and pressure, andwithdrawing residual liquor. from the pressure vessel.

4. The continuous method of producing ferrous sulphate monohydrate frompickle liquor which includes heating the pickle liquor to aboveapproximately 290 F. while maintaining the liquor at a pressuresuflicient to prevent formation of steam, directing flow 01' the heatedpickle liquor into an enlarged pressure vessel so as to reduce thevelocity of the pickle liquor and reversing the flow in said pressurevessel so as to cause the crystals formed at said temperature toseparate by sedimentation, separating out the ferrous sulphate 40monohydrate thus formed while maintaining the liquor at the abovetemperature and pressure,

withdrawing the ferrous sulphate monohydrate from the bottom or thepressure vessel, and withdrawing resldual liquor from the pressurevessel.

. I DEXTER EDGE.

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